The first ever pictures of the northern and southern auroras expanding and brightening in unison have confirmed the theory that auroras occur in mirror image.

During a space weather storm last week, NASA's Polar spacecraft captured on film the Earth's conjugate auroras - the aurora australis and the aurora borealis dancing in near mirror image of each other.

"For the first time, the northern and southern auroral ovals were observed simultaneously with enough resolution to confirm that the northern and southern auroras are mirror images of each other on a global scale," says Dr John Sigwarth, a space physicist at the University of Iowa who helped design and operate the Visible Imaging System that captured the images.

"Further analysis of these images should help us determine if all of the auroral features are exactly mirrored down to the finest details" he says.

Preliminary research suggests that while the auroras mimic each other on broad scales, there are also some fine features that do not match.

Auroral displays occur within large rings surrounding the poles with diameters of roughly 4,000km.

"This ability to film both auroras simultaneously is exciting because it will help scientists better understand the generation of auroras at a global scale, as well as providing some breathtaking images," says Dr Lech Hajkowicz, an auroral physicist recently retired from the University of Queensland.

The first recorded sighting of mirror - or conjugate - auroras was made during the expeditions of Captain James Cook around Australia and the South Pacific over 200 years ago on the HMS Endeavour.

Cook's crew recorded that "a phenomenon appeared in the heavens in many things resembling the aurora borealis". Historical documents from China later revealed that an aurora was observed on the same night, 16 September 1770, in the Northern Hemisphere.

Since then scientists have conducted ground and aircraft studies of simultaneous auroras but this is the first time they have been able to capture images of both hemispheres at the same time.

The best place to observe auroras in Australia is Macquarie Island, according to Dr Hajkowicz. Other places from which the aurora can be seen include Tasmania and Southern Victoria although only during large magnetic storms, which happen infrequently.